Generally, a laundry treating apparatus includes a cabinet defining an external appearance; a tub mounted in the cabinet; a drum rotatably provided in the tub and washing clothes or laundry; and a motor fixed to the drum by using a shaft penetrating the tub to rotate the drum.
The drum is likely to rotate while failing to keep dynamic equilibrium or dynamic balance according to the location of the laundry loaded in the drum.
The dynamic equilibrium means a state where a centrifugal force of a rotating rotary body or the moment created by the centrifugal force becomes zero with respect to a rotation axis. When mass distribution is consistent with respect to a rotation shaft, a rigid body rotating on the rotation axis keeps dynamic equilibrium.
When the drum is rotated with laundry loaded therein, it can be understood that dynamic equilibrium is kept in the laundry treating apparatus when mass distribution of laundry with respect to the shaft of the drum is within an allowable range (when the drum is rotated while vibrating within an allowable range).
Dynamic unbalance of the laundry treating apparatus means a state where mass distribution is not consistent with respect to the shaft of the drum when the drum is being rotated, in other words, where laundry is not distributed in the drum uniformly or consistently/
The drum being rotated in unbalance is vibrated by the rotation and the vibration of the drum is transferred to the tub or cabinet only to generate noise disadvantageously.
A certain conventional laundry treating apparatus includes a balancing unit for compensating the unbalance of the drum. Balancing units provided in the conventional treating apparatuses the ball or liquid balancers having balls or liquid provided in a housing fixed in the drum.
Such the unbalanced drum is characterized to be the fastest when the laundry causing the unbalance passes the lowermost point of drum rotation locus and the slowest when passing the uppermost point.
Accordingly, when a ball or liquid balancer provided in the conventional laundry treating apparatus is configured to control unbalance by moving a ball or liquid toward the lowermost point of the drum rotation locus, when the laundry causing unbalance is moved toward the uppermost point of the drum rotation locus.
However, the control method for the unbalance mentioned above cannot be expected in a transient vibration state which is before the vibration of the drum reaches a steady state.
Moreover, it is difficult for the conventional balancing unit to overcome the unbalance right away after unbalance is sensed (settle the unbalance positively).